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Versions: 00 01 02 03 04 05 06 RFC 5210

Network Working Group                                              J. Wu
Internet-Draft                                                     J. Bi
Intended status: Experimental                                      X. Li
Expires: September 14, 2008                                       G. Ren
                                                                   K. Xu
                                                     Tsinghua University
                                                             M. Williams
                                                        Juniper Networks
                                                            Mar 13, 2008

                  SAVA Testbed and Experiences to Date

Status of this Memo

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   This Internet-Draft will expire on September 14, 2008.

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   Since the Internet uses destination-based packet forwarding,
   malicious attacks have been launched using spoofed source addresses.
   In an effort to enhance the Internet with IP source address
   validation, we prototyped an implementation of the IP Source Address
   Validation Architecture (SAVA) and conducted the evaluation on an
   IPv6 network.  This document reports our prototype implementation and
   the test results, as well as the lessons and insights gained from our

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4

   2.  A Prototype SAVA Implementation  . . . . . . . . . . . . . . .  5
     2.1.  Solution Overview  . . . . . . . . . . . . . . . . . . . .  5
     2.2.  IP Source Address Validation in the Access Network . . . .  6
     2.3.  IP Source Address Validation at Intra-AS/Ingress Point . .  8
     2.4.  IP Source Address Validation in Inter-AS Case
           (Neighboring AS) . . . . . . . . . . . . . . . . . . . . .  8
     2.5.  IP Source Address Validation in Inter-AS Case
           (Non-Neighboring AS) . . . . . . . . . . . . . . . . . . . 11

   3.  SAVA Testbed . . . . . . . . . . . . . . . . . . . . . . . . . 14
     3.1.  CNGI-CERNET2 . . . . . . . . . . . . . . . . . . . . . . . 14
     3.2.  SAVA Testbed on CNGI-CERNET2 Infrastructure  . . . . . . . 14

   4.  Test Experience and Results  . . . . . . . . . . . . . . . . . 17
     4.1.  Test Experience  . . . . . . . . . . . . . . . . . . . . . 17
     4.2.  Test Results . . . . . . . . . . . . . . . . . . . . . . . 17

   5.  Limitations and Issues . . . . . . . . . . . . . . . . . . . . 19
     5.1.  General Issues . . . . . . . . . . . . . . . . . . . . . . 19
     5.2.  Security Issues  . . . . . . . . . . . . . . . . . . . . . 20
     5.3.  Protocol Details . . . . . . . . . . . . . . . . . . . . . 20

   6.  Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 22

   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 23

   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 24

   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25

   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 26

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     10.2. Informative References . . . . . . . . . . . . . . . . . . 26

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
   Intellectual Property and Copyright Statements . . . . . . . . . . 29

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1.  Introduction

   By design the Internet forwards data packets solely based on the
   destination IP address.  The source IP address is not checked during
   the forwarding process in most cases.  This makes it easy for
   malicious hosts to spoof the source address of the IP packet.  We
   believe that it would be useful to enable the Internet security to
   enforce the validity of the source IP address for all the packets
   being forwarded. .

   Enforcing the source IP address validity can help us achieve the
   following goals:

   o  The packets which carry spoofed source addresses will not be
      forwarded, making it impossible to launch network attacks with
      spoofed source addresses.

   o  The packets which hold a correct source address can be traced back
      accurately.  This can benefit network diagnosis, management,
      accounting and applications.

   As part of the effort in developing a Source Address Validation
   Architecture (SAVA), we have implemented a SAVA prototype on an
   operational network, a native IPv6 backbone network of the China Next
   Generation Internet project, and conducted evaluation experiments.
   In this document we first describe our prototype solutions and then
   report our experimental results.  We hope that this document can
   provide useful insights to those interested in the subject, and can
   serve as an initial input to future IETF effort in the same area.

   In recent years there have been a number of research and engineering
   efforts to design IP source address validation mechanisms, such
   as[RFC2827][Park01][Li02][Brem05][Snoe01].  Our SAVA prototype
   implementation was inspired by some of the schemes from the proposed
   or existing solutions.  The prototype implementation and experimental
   results presented in this report serve only as an input, and by no
   means pre-empt any solution development that may be carried out by
   future IETF effort.  Indeed, the presented solutions are experimental
   approaches and have a number of limitations as discussed in sections
   5 and 6.

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2.  A Prototype SAVA Implementation

2.1.  Solution Overview

   In the Internet at large, it is unrealistic to expect any single IP
   source address validation mechanism to be universally supported.
   Different operators and vendors may choose to deploy/develop
   different mechanisms to achieve the same end, and there need to be
   different mechanisms to solve the problem at different places in the
   network.  Furthermore, implementation bugs or configuration errors
   can also render the intended implementation in-effective.  Therefore
   our prototype SAVA implementation is a combination of multiple
   coexisting and cooperating mechanisms.  More specifically, we
   implement source IP address validation at three levels: access
   network source address validation; intra-AS source address
   validation; and inter-AS source address validation, as shown in
   Figure 1.The system details can be found in[WRL2007].
                  __ ____                          __ ____
              .-''       `':                   .-''       `':
              |             |                  |             |
              |   +-+----+  |   Inter-AS SAV   |   +-+----+  |
              |   |Router+--+------------------+---|Router+  +
              |   +--.---+  |                  |   +--.---+  |
   Intra-AS   |      |      |       Intra-AS   |      |      |
      SAV     |   +--+---+  |          SAV     |   +--+---+  |
              |   |Router|  |                  |   |Router|  |
              '_  +--.---+  _                  '_  +--.---+  _
                `'---|---'''                     `'---|---'''
                 _.--|-----.                      _.--|-----.
             ,-''    |      `--.              ,-''    |      `--.
           |'+-----------------+`|          |'+-----------------+`|
           | |     Router      | |          | |     Router      | |
           | ++----------------+ |          | ++----------------+ |
    Access |  |      |        |  |   Access |  |      |        |  |
    Network|  | +------++------+ |   Network|  | +------++------+ |
     SAV   |  | |Switch||Router| |    SAV   |  | |Switch||Router| |
           |  | +------++------+ |          |  | +------++------+ |
           |  |      |        |  |          |  |      |        |  |
           |+-+--+ +----+ +----+ |          |+-+--+ +----+ +----+ |
           ||Host| |Host| |Host| |          ||Host| |Host| |Host| |
           `.----+ +----+ +----+,'          `.----+ +----+ +----+,'
             `--.           _.-'              `--.           _.-'
                 `--------''                      `--------''
   Key: SAV== Source Address Validation

                        Figure 1: Solution Overview

   It is important to enforce IP source address validity at the access

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   network.  That is, when an IP packet is sent from a host, the
   routers, switches or other devices should check to make sure that the
   packet carries a valid source IP address.  If this access network
   source address validation is missing, then a host may be able to
   spoof the source IP address which belongs to another local host.

   We use the term "intra-AS source address validation" to mean the IP
   source address validation at the attachment point of an access
   network to its provider network, also called the ingress point.  IP
   source address validation at ingress points can enforce the source IP
   address correctness at the IP prefix level, assuming the access
   network owns one or more IP address blocks.  This practice has been
   adopted as the Internet Best-Current-Practice [RFC2827][RFC3704].
   Even in the absence of the access network source address checking,
   this ingress checking can still prevent the hosts within one access
   network from spoofing IP addresses belonging to other networks.

   In theory, everyone would do validation at the access network level
   and again at the intra-AS level.  In reality, some packets will get
   validated and some will not get validated.  As a result, the
   different levels provide additional layers of defense.

   Inter-AS IP source address validation refers to mechanisms that
   enforce packet source address correctness at AS boundaries.  The
   first two steps of source address validation utilize the network
   physical connectivity of the access network and the ingress points.
   Because the global Internet has a mesh topology, and because
   different networks belong to different administrative authorities, IP
   source address validation at Inter-AS level becomes more challenging.
   Nevertheless we believe this third level of protection is necessary
   to detect packets with spoofed source addresses, when the first two
   levels of source address validation are missing or ineffective.

   In the rest of this section we describe the specific mechanisms
   implemented at each of the three levels in detail.

2.2.  IP Source Address Validation in the Access Network

   At the access network level, the solution will make sure the host
   inside the access network cannot use the source address of another
   host.  The host address should be a valid address assigned to the
   host statically or dynamically.  The solution implemented in the
   experiment provides such a function for Ethernet networks.  A layer-3
   source address validation device (SAVA Device) for the access network
   (the device can be a function inside the CPE router or a separate
   device) is deployed at the exit of the access network.  Source
   address validation agents (SAVA Agents) are deployed inside the
   access network.  (In fact these agents could be a function inside the

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   first hop router/switch connected to the hosts.)  A set of protocols
   was designed for communication between the host, SAVA Agent and SAVA
   Device.  Only a packet originating from the host that was assigned
   that particular source address may pass through the SAVA Agent and
   SAVA Device.

   Two possible deployment variants exist.  In one variant an agent is
   mandatory and each host is attached to the agent on a dedicated
   physical port.  In another variant hosts are required to perform
   network access authentication and generate key material needed to
   protect each packet.  In this second variant the agent is optional.

   The key function of the first variant is to create a dynamic binding
   between a switch port and valid source IP address, or a binding
   between MAC address, source IP address and switch port.  In the
   prototype, this is established by having hosts employ a new address
   configuration protocol that the switch is capable of tracking.

   Note: In a production environment the approach in the prototype would
   not be sufficient due to reasons discussed in Section 5.

   In this variant, there are three main participants: Source Address
   Request Client (SARC) on the host, Source Address Validation Proxy
   (SAVP) on the switch, and Source Address Management Server (SAMS).
   The solution follows the basic steps below:

   1.  The SARC on the end host sends an IP address request.  The SAVP
       on the switch relays this request to the SAMS and records the MAC
       address and incoming port.  If the address has already been
       predetermined by the end host, the end host still needs to put
       that address in the request message for verification by SAMS.

   2.  After the SAMS receives the IP address request then allocates a
       source address for that SARC based on the address allocation and
       management policy of the access network, it stores the allocation
       of the IP address in the history database of SAMS for traceback,
       then sends response message containing the allocated address to
       the SARC.

   3.  After the SAVP on the access switch receives the response, it
       binds the IP address and the former stored MAC address of the
       request message with the switch port on the binding table.  Then,
       it forwards the issued address to SARC on the end host.

   4.  The access switch begins to filter packets sent from the end
       host.  Packets which do not conform to the tuple (IP address,
       Switch Port) are discarded.

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   The main idea of the second variant is to employ key material from
   network access authentication for some additional validation process.
   A session key is derived for each host connecting to the network, and
   each packet sent by the host has cryptographic protection that
   employs this session key.  Having established which host the packet
   comes from, it becomes again possible to track that the addresses
   allocated to the host and used by the host match.  The mechanism
   details can be found in [XBW07], but the the process follows these
   basic steps:

   1.  When a host wants to establish connectivity, it first needs to
       perform network access authentication.

   2.  The network access devices provide the SAVA Agent (often co-
       located) a session key S. This key is further distributed to the
       SAVA Device.  The SAVA Device binds the session key and the
       host's IP address.

   3.  When the host sends packet M to somewhere outside the access
       network, either the host or the SAVA Agent needs to generate a
       message authentication code for each using key S and packet M. In
       the prototype, the message authentication code is carried in an
       experimental IPv6 extension header.

   4.  The SAVA Device uses the session key to authenticate the
       signature carried in the packet so that it can validate the
       source address.

2.3.  IP Source Address Validation at Intra-AS/Ingress Point

   We adopted the solution of the source address validation of IP
   packets at ingress points described in [RFC2827]and[RFC3704]; the
   latter describes source address validation at the ingress points of
   multi-homed access networks.

2.4.  IP Source Address Validation in Inter-AS Case (Neighboring AS)

   Our design for the Inter-AS Source Address Validation aimed at the
   following characteristics: It should cooperate among different ASes
   with different administrative authorities and different interests.
   It should be light-weight to support high throughput and not to
   influence forwarding efficiency.

   The inter-AS level of SAVA can be classified into two sub-cases:

   o  Two SAVA-compliant ASes exchanging traffic are directly connected;

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   o  Two SAVA-compliant ASes are separated by one or more intervening,
      SAVA-non-compliant providers.

                                        | AIMS   |
   --------------                   -----------|-----
   |  AS-4       |--------  --------|    AS-1  |    |-------     Global
   | ------      |ASBR,VE|->|ASBR,VE|    ------|-   |ASBR,VE|--->IPv6
   | |VRGE|      |--------  --------|    | VRGE |   |-------     Network
   | ------      |                  |    --------   |
   ---------------            ----- -----------------
                              |ASBR,VE|    |ASBR,VE|
                              ---------    ---------
                               /             |
                              /              |
                             /               |
                            /                |
                        ----------        --------
                        |ASBR, VE|        |ASBR,VE|
                   ---------------      -------------
                   |   AS-2      |      |  AS-3     |
                   |  -----      |      |   -----   |
                   |  |VRGE|     |      |  |VRGE|   |
                   |  -----      |      |  ------   |
                   ---------------      -------------

   Key: AIMS == AS-IPv6 prefix Mapping Server, VRGE == Validation Rule
   Generating Engine, VE == Validating Engine, ASBR = AS Border Router,
   VR==Validation Rule

               Figure 2: Inter-ISP (Neighboring AS) Solution

   An AS relation based mechanism is used for neighboring SAVA-compliant
   ASes.  The basic ideas of this AS-relation based mechanism are as
   follows.  It builds a VR table that associates each incoming
   interface of the router with a set of valid source address blocks,
   and then uses it to filter spoofed packets.

   In the solution implemented on the testbed, the solution for the
   validation of IPv6 prefixes is separated into three functional
   modules: The Validation Rule Generating Engine (VRGE), the Validation
   Engine (VE) and the the AS-IPv6 prefix Mapping Server(AIMS).
   Validation rules (VR) that are generated by the VRGE are expressed as
   IPv6 address prefixes.

   The VRGE generates validation rules which are derived according to

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   the table shown in figure 3, and each AS has a VRGE.  The VE loads
   validation rules generated by VRGE to filter packets passed between
   ASes (in the case of Figure 2, from neighboring ASes into AS-1).  In
   the SAVA testbed, the VE is implemented as a simulated L2 device on a
   Linux-based machine inserted into the data path just outside each
   ASBR interface that faces a neighboring AS, but in a real-world
   implementation, it would probably be implemented as a packet
   filtering set on the ASBR.  The AS-IPv6 prefix mapping server is also
   implemented on a Linux machine and derives a mapping between IPv6
   prefix and the AS number of that prefix.
|   \Export| Own        | Customer's| Sibling's | Provider's | Peer's     |
|To  \     | Address    | Address   | Address   | Address    | Address    |
| Provider |      Y     |    Y      |     Y     |            |            |
| Customer |      Y     |    Y      |     Y     |     Y      |     Y      |
| Peer     |      Y     |    Y      |     Y     |            |            |
| Sibling  |      Y     |    Y      |     Y     |     Y      |     Y      |

              Figure 3: AS-Relation Based Inter-AS Filtering

   Different ASes exchange and transmit VR information using the AS-
   Relation Based Export Rules in the VRGE.  As per Figure 3, an AS
   exports the address prefixes of its own, its customers, its
   providers, its siblings and its peers to its customers and siblings
   as valid prefixes, while it only exports the address prefixes of its
   own, its customers and its siblings to its providers and peers as
   valid prefixes.  With the support of AS Number to IPv6 Address
   Mapping service, only AS numbers of valid address prefixes are
   transferred between ASes and the AS number is mapped to address
   prefixes at the VRGE.  Only changes of AS relation and changes of IP
   address prefixes belonging to an AS require the generation of VR

   The procedure's principle steps are as follows (Seeing from AS-1 in
   Figure 2):

   1.  When the VRGE has initialized, it reads its neighboring SAVA-
       compliant AS table and establishes connections to all the VEs in
       its own AS.

   2.  The VRGE initiates a VR renewal.  According to its exporting
       table, it sends its own originated VR to VRGEs of neighboring
       ASes.  In this process, VR are expressed as AS numbers.

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   3.  When a VRGE receives the new VR from its neighbor, it uses its
       own export table to decide whether it should accept the VR and,
       if it accepts a VR, whether or not it should re-export the VR to
       other neighboring ASes.

   4.  If the VRGE accepts a VR, it uses the AIMS to transform AS-
       expressed VR into IPv6 prefix-expressed VR.

   5.  The VRGE pushes the VR to all the VEs in its AS.

   The VEs use these prefix-based VRs to validate the source IP
   addresses of incoming packets.

2.5.  IP Source Address Validation in Inter-AS Case (Non-Neighboring AS)

   In the case where two ASes do not exchange packets directly, it is
   not possible to deploy a solution like that in the previous section.
   However, it is highly desirable for non-neighboring ISPs to be able
   to form a trust alliance such that packets leaving one AS will be
   recognized by the other and inherit the validation status they
   possessed on leaving the first AS.  There is more than one way to do
   this.  For the SAVA experiments to date, a signature method has been
   used.  This solution is inspired by the work [Brem05].  The key
   elements of this light-weight signature based mechanism are as
   follows: For each pair of SAVA-compliant ASes, there is a pair of
   unique temporary signatures.  All SAVA-compliant ASes together form a
   SAVA AS Alliance.  When a packet is leaving its own AS, if the
   destination IP address belongs to an AS in the SAVA AS Alliance, the
   edge router of this AS looks up for the signature based on the
   destination AS number, and tags a signature to the packet.  When a
   packet arrives at the destination AS, if the source address of the
   packet belongs to an AS in the SAVA AS Alliance, so the edge router
   of the destination AS searches its table for the signature using the
   source AS number as the key and the signature carried in the packet
   is verified and removed.  This particular method uses a light-weight
   signature.  For every packet forwarded, the signature can be put in
   an IPv6 hop-by-hop extension header.  It bis reasonable to use a 128-
   bit shared random number as the signature to save the processing
   overhead of using a cryptographic method to generate the signature.

   The benefit of this scheme compared to merely turning on local
   address validation such as RFC 2827 is as follows.  When local
   address validation is employed within a group of networks, they can
   be assured that their networks do not send spoofed packets.  However,
   other networks may still do this.  With the above scheme,however,
   this capability is reduced.  If someone outside the alliance spoofs a
   packet using a source address from someone within the alliance, the
   members of the alliance refuse to accept such a packet.

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              .-----------------+.REG |-----------------.
              |                 +-----+                 |
              |                                         |
        ,-----+--------                          ,------+-------
      ,'     `|        `.                      ,'     ` |       `.
     /        |         \                     /         |         \
    /         |          \                   /          |          \
   ;       +--'--+      +----+             +----+     +-----+       ;
   |       | ASC +------+ASBR|             |ASBR+-----+ ASC |       |
   :       +--.--+      +----+`            +----+     +--+--+       :
    \         |__________________________________________|         /
     \                   /                    \                   /
      `.               ,'                      `.               ,'
        '-------------'                          '-------------'
             AS-1                                     AS-2
   KEY: REG == Registration Server, ASC == AS Control Server, ASBR == AS
   Border Router.

             Figure 4: Inter-AS (Non-neighboring AS) Solution

   There are three major components in the system: the Registration
   Server (REG), the AS Control Server (ASC), and the AS Border Router

   The Registration Server is the "center" of the trust alliance (TA) .
   It maintains a member list for the TA.  It performs two major

   o  Processes requests from the AS Control Server, to get the member
      list for the TA.

   o  When the member list is changed, notifies each AS Control Server.

   Each AS deploying the method has an AS Control Server.  The AS
   Control Server has three major functions:

   o  Communicates with the Registration Server, to get the up-to-date
      member list of TA.

   o  Communicates with the AS Control Server in other member AS in the
      TA, to exchange updates of prefix ownership information, and to
      exchange signatures.

   o  Communicates with all AS Border routers of the local AS, to
      configure the processing component on the AS Border routers.

   The AS Border Router does the work of adding signature to the packet

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   at the sending AS, and the work of verifying and removing the
   signature at the destination AS.

   In the design of this system, in order to decrease the burden on the
   REG, most of the control traffic happens between ASCs.

   The signature needs to be changed frequently, Although the overhead
   of maintaining and exchanging signatures between AS pairs is not
   O(N^2), but O(N), the traffic and processing overhead increase as the
   number of ASes increases.  Therefore an automatic signature changing
   method is utilized in this solution.

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3.  SAVA Testbed


   The prototypes of our solutions for SAVA are implemented and tested
   on CNGI-CERNET2.  CNGI-CERNET2 is one of the China Next Generation
   Internet (CNGI) backbones.  CNGI-CERNET2 connects 25 core nodes
   distributed in 20 cities in China at speeds of 2.5-10 Gb/s.  The
   CNGI-CERNET2 backbones are IPv6-only networks, not a mixed IPv4/IPv6
   infrastructure.  The CNGI-CERNET2 backbones, CNGI-CERNET2 CPNs, and
   CNGI-6IX all have globally unique AS numbers.  Thus a multi-AS
   testbed environment is provided.

3.2.  SAVA Testbed on CNGI-CERNET2 Infrastructure

   It is intended that eventually the SAVA testbed will be implemented
   directly on the CNGI-CERNET2 backbone, but in the early stages the
   testbed has been implemented across 12 universities connected to
   CNGI-CERNET2.  This is because first, some of the algorithms need to
   be implemented in the testbed routers themselves and to date they
   have not been implemented on any of the commercial routers forming
   the CNGI-CERNET2 backbone.  Second, since CNGI-CERNET2 is a
   operational backbone, any new protocols and networking techniques
   need to be tested in a non- disruptive way.

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                             ,'  \                            _,...._
                            ,'    \____---------------+     ,'Beijing`.
                            /      \  | Inter-AS SAV  |-----| Univ    |
    +---------------+     |         | +---------------+     `-._____,'
    | Inter-AS SAV  +-----|         |
    +------.--------+     |  CNGI-  |                         _,...._
           |              | CERNET2 |__---------------+     ,Northeast`.
           |              |         | |Inter-AS SAV   |-----| Univ    |
   Tsinghua|University    | Backbone| +---------------+     `-._____,'
        ,,-|-._           |         |
      ,'   |   `.         |         |
    ,'+---------+\        |         |
   |  |Intra-AS | |       |         |      ...
   |  |   SAV   | |       |         |
   |  +---------+ |       |         |
   |       |      |       |         |                         _,...._
   |  +---------+ |       |         |__---------------+     ,Chongqing`.
   |  | Access  | |       |         | |Inter-AS SAV   |-----|Univ     |
   |  | Network | |       |         | +---------------+     `-._____,'
   |  |  SAV    | |       |         |
    \ +---------+.'        \       .'
     \          ,'          \      |
      `.      ,'             \    /
        ``---'                -_,'
   KEY: SAV=Source Address Validation

                    Figure 5: CNGI-CERNET2 SAVA Testbed

   In any case, the testbed is fully capable of functional testing of
   solutions for all parts of the SAVA solution.  This includes testing
   procedures for ensuring the validity of IPv6 source addresses in the
   access network and in packets sent from the access network to an IPv6
   service provider, packets sent within one service provider's network,
   packets sent between neighboring service providers and packets sent
   between service providers separated by an intervening transit

   The testbed is distributed across 12 universities connected to CNGI-

   Each of the university installations is connected to the CNGI-CERNET2
   backbone through a set of inter-AS Source Address Validation
   prototype equipment and traffic monitoring equipment for test result

   One of the univeristy installations acts as the main site and is most
   fully-featured, with inter-AS, intra-AS and access network level

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   validation all able to be tested.  In addition, a suite of
   applications that could be subject to spoofing attacks or which can
   be subverted to carry out spoofing attacks are installed on a variety
   of servers.

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4.  Test Experience and Results

   The solutions outlined in section 2 have been implemented on the
   testbed described in section 3.  Successful testing of all solutions
   has been carried out, as detailed in the following sections.

4.1.  Test Experience

   For each of the test scenarios, we have tested many cases.  Taking
   Inter-AS (non-neighboring AS) SAVA solution test as an example, we
   classified the test cases into three classes: normal class, dynamic
   class and anti-spoofing class.

   1.  For normal class, there are three cases: Adding Signature Test,
       Removing Signature Test and Forwarding packets with valid source

   2.  For dynamic class, there are four cases: Updating the signature
       between ASes, The protection for a newly joined member AS, Adding
       address space and Deleting address space.

   3.  For anti-spoofing class, there is one case: Filtering of packets
       with forged IP address.

   As is shown in Fig.5, we have "multiple-fence" design for our SAVA
   testbed.  If source address validation is deployed in the access
   network, we can get a host granularity validation.  If source address
   validation is deployed at intra-AS level, we can guarantee that the
   packets sent from this point have a correct IP prefix.  If source
   address validation is deployed at inter-AS level, we can guarantee
   that the packets sent from this point are from the correct AS.

4.2.  Test Results

   1.  The test results are consistent with the expected ones.  For an
       AS which has fully-featured SAVA deployment with inter-AS,
       intra-AS and access network level validation, packets that do not
       hold an authenticated source address will not be forwarded in
       network.  As a result, it is not possible to launch network
       attacks with spoofed source addresses.  Moreover, the traffic in
       the network can be traced back accurately.

   2.  For the Inter-AS (non-neighboring AS) SAVA solution, during the
       period of signature update, the old and the new signature are
       both valid for source address validation, thus there is no packet

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   3.  For the Inter-AS (non-neighboring AS) SAVA solution, the
       validation function is implemented in software on a device
       running Linux, which simulates the source address validation
       functions of a router interface.  It is a layer-two device
       because it has to be transparent to router interface, During the
       test, If the devices were connected directly, it could achieve a
       normal line rate forwarding.  If the devices were connected with
       routers from another vendor, it could only achieve a very limited
       line speed.  The reason is that the signatures are added on the
       IPv6 hop-by-hop option header and many current routers can handle
       the hop-by-hop options only at a limited rate.

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5.  Limitations and Issues

   There are several issues both within this overall problem area and
   with the particular approach taken in the experiment.

5.1.  General Issues

   There is a long standing debate about whether the lack of universal
   deployment of source address validation is a technical issue that
   needs a technical solution, or if mere further deployment of existing
   tools (such as RFC 2827) would be a more cost effective way to
   improve the situation.  Further deployment efforts of this tool have
   proved to be slow, however.  Some of solutions prototyped in this
   experiment allow a group of network operators to have additional
   protection for their networks while waiting for universal deployment
   of simpler tools in the rest of the Internet.  This allows them to
   prevent spoofing attacks that the simple tools alone would not be
   able to prevent, even if already deployed within the group.

   Similarly, since a large fraction of current denial-of-service
   attacks are employing legitimate IP addresses belonging to botnet
   clients, even universal deployment of better source address
   validation techniques would be unable to prevent these attacks.
   However, tracing these attacks would be easier given that there would
   be more reliance on the validity of source address.

   There is also a question about the right placement of the source
   address validation checks.  The simplest model is placing the checks
   on the border of a network.  Such RFC 2827-style checks are more
   widely deployed than full checks ensuring that all addresses within
   the network are correct.  It can be argued that it is sufficient to
   provide such a coarse granularity checks, because this makes it at
   least possible to find the responsible network administrators.
   However, depending on the type of a network in question, those
   administrators may or may not find it easy to track the specific
   offending machines or users.  It is obviously required that the
   administrators have a way to trace offending equipment or users --
   even if the network does not block spoofed packets in real-time.

   New technology for address validation would also face a number of
   deployment barriers.  For instance, all current technology can be
   locally and independently applied.  A system that requires global
   operation (such as the Inter-AS validation mechanism) would require
   significant coordination, deployment synchronization, configuration,
   key setup, and other issues, given the number of ASes.

   Similarly, deploying host-based access network address validation
   mechanisms requires host changes, and can generally be done only when

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   the network owners are in control of all hosts.  Even then,
   availability of the host changes for all types of products and
   platforms would likely prevent universal deployment even within a
   single network.

   There may be also be significant costs involved in some of these
   solutions.  For instance, in an environment where access network
   authentication is normally not required, employing an authentication-
   based access network address validation would require deployment of
   equipment capable of this authentication as well as credentials
   distribution for all devices.  Such undertaking is typically only
   initiated after careful evaluation of the costs and benefits

   Finally, all the presented solutions have issues in situations that
   go beyond a simple model of a host connecting to a network via the
   same single interface at all times.  Multihoming, failover and some
   forms of mobility or wireless solutions may collide with the
   requirements of source address validation.  In general, dynamic
   changes to the attachment of hosts and topology of the routing
   infrastructure is something that would have to be handled in
   production environment.

5.2.  Security Issues

   The security vs. scalability of the signatures in the Inter-AS (non-
   neighboring AS) SAVA solution presents a difficult tradeoff.  Some
   analysis about the difficulty of guessing the signature between two
   AS members was discussed in [Brem05].  It is relatively difficult,
   even with using a random number as a "signature".  The difficulty of
   guessing can be increased by increasing the length of the signature.

   In any case, the random number approach is definitely vulnerable to
   attackers who are on the path between the two ASes.

   On the other hand, using an actual cryptographic hash in the packets
   will cause a significant increase in the amount of effort needed to
   forward a packet.  In general, addition of the option and the
   calculation of the signature consumes valuable resources on the
   forwarding path.  This resource usage comes on top of everything else
   that modern routers need to do at ever increasing line speeds.  It is
   far from clear that costs are worth the benefits.

5.3.  Protocol Details

   In current CNGI-CERNET2 SAVA testbed, a 128-bit signature is placed
   in IPv6 a new hop-by-hop option header.  The size of the packets
   increases with the signatures.  This by itself is expected to be

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   acceptable, if the network administrator feels that the additional
   protection is needed.  However, the size increases may result in MTU
   issues similar to those present in tunnels.  Given the choice to use
   an IPv6 IPv6 hop-by-hop option has to be looked at by all intervening
   routers.  While in theory this should pose no concern, the test
   results show that many current routers handle hop-by-hop options with
   a much reduced throughput compared to normal traffic.

   The Inter-AS (neighboring AS) SAVA solution is based on AS relation,
   thus it cannot synchronized with the dynamics of route changes very

   The access network address validation solution is merely one option
   among many.  Solutions appear to depend highly on the chosen link
   technology and network architecture.  For instance, source address
   validation on point-to-point links is easy and has generally been
   supported by implementations for years.  Validation in a shared
   networks has been more problematic, but is increasing in importance
   given the use Ethernet technology across administrative boundaries
   (such as in DSL).  In any case, the prototyped solution has a number
   of limitations, including the decision to use a new address
   configuration protocol.  In a production environment the approach in
   the prototype would not be sufficient; a solution integrated to
   existing protocols, servers, and tools would be needed.

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6.  Conclusion

   Several conclusions can be made from the experiment.

   First, the experiment is a proof that a working system can be built
   on the basis of the loosely-coupled domains and "multiple-fence"
   design for source address validation.  The solution allows different
   validation granularities, and also allows different providers to use
   different solutions.  The coupling of components at different levels
   of granularity can be loose enough to allow component substitution.

   Incremental deployment is another design principle that was used in
   the experiment.  The tests have demonstrated that benefit is derived
   even when deployment is incomplete, which gives providers an
   incentive to be early adopters.

   The experiment also provided a proof of concept for the switch-based
   local subnet validation, network authentication based validation,
   filter-based Inter-AS validation, and signature-based Inter-AS
   validation mechanisms.

   Nevertheless, as discussed in the previous section, there are a
   number of limitations, issues, and question marks in the prototype
   designs and the overall source address validation space.

   It is our hope that some of the experiences will help vendors and the
   Internet standards community in these efforts.  Future work in this
   space should attempt to answer some of the issues raised in Section
   5.  Some of the key issues going forward include:

   o  Scalability questions and per-packet operations.

   o  Protocol design issues, such as integration to existing address
      allocation mechanisms, use of hop-by-hop headers, etc.

   o  Cost vs. benefit questions.  These may be ultimately answered only
      by actually employing some of these technologies in production

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7.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an

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8.  Security Considerations

   The purpose of the draft is to report experimental results.  The
   security considerations of the solution mechanisms of testbed are not
   mentioned in this document.

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9.  Acknowledgements

   This experiment was conducted among 12 universities, namely Tsinghua
   University, Beijing University, Beijing University of Post and
   Telecommunications, Shanghai Jiaotong University, Huazhong University
   of Science and Technology in Wuhan, Southeast University in Nanjing,
   and South China University of Technology in Guangzhou, Northeast
   University in Shenyang, Xi'an Jiaotong University, Shandong
   University in Jinan, University of Electronic Science and Technology
   of China in Chengdu and Chongqing University.  The authors would like
   to thank everyone involved in this effort in these universities.

   The authors would like to thank Jari Arkko and Lixia Zhang for their
   detailed review comments on this draft, and thank Paul Ferguson and
   Ron Bonica for their valuable advices on the solution development and
   the testbed implementation.

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10.  References

10.1.  Normative References

   [RFC2827]  Paul, F. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, May 2000.

   [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed
              Networks", BCP 84, RFC 3704, 2004.

10.2.  Informative References

   [Brem05]   Bremler-Barr, A. and H. Levy, "Spoofing Prevention
              Method", INFOCOM 2005.

   [Li02]     Li,, J., Mirkovic, J., Wang, M., Reiher, P., and L.
              Zhang, "SAVE: Source Address Validity Enforcement
              Protocol", INFOCOM  2002.

   [Park01]   Park, K. and H. Lee, "On the effectiveness of route-based
              packet filtering for distributed DoS attack prevention in
              power-law internets", SIGCOMM 2001.

   [Snoe01]   Snoeren, A., Partridge, C., Sanchez, L., and C.
              Jones......, "A Hash-based IP traceback", SIGCOMM 2001.

   [WRL2007]  Wu, J., Ren, G., and X. Li, "Source Address Validation:
              Architecture and Protocol Design", ICNP 2007.

   [XBW07]    Xie, L., Bi, J., and J. Wu, "An Authentication based
              Source Address Spoofing Prevention Method Deployed in IPv6
              Edge Network", ICCS 2007.

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Authors' Addresses

   Jianping Wu
   Tsinghua University
   Computer Science, Tsinghua University
   Beijing  100084

   Email: jianping@cernet.edu.cn

   Jun Bi
   Tsinghua University
   Network Research Center, Tsinghua University
   Beijing  100084

   Email: junbi@cernet.edu.cn

   Xing Li
   Tsinghua University
   Electronic Engineering, Tsinghua University
   Beijing  100084

   Email: xing@cernet.edu.cn

   Gang Ren
   Tsinghua University
   Computer Science, Tsinghua University
   Beijing  100084

   Email: rg03@mails.tsinghua.edu.cn

   Ke Xu
   Tsinghua University
   Computer Science, Tsinghua University
   Beijing  100084

   Email: xuke@csnet1.cs.tsinghua.edu.cn

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   Mark I. Williams
   Juniper Networks
   Suite 1508, W3 Tower, Oriental Plaza, 1 East Chang'An Ave
   Dong Cheng District, Beijing  100738

   Email: miw@juniper.net

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